A strut-type suspension used in a front wheel of a four-wheeled vehicle generally has a structure in which a strut assembly incorporating a hydraulic shock absorber in an outer cylinder formed integrally with a main shaft is combined with a coil spring. In such suspensions, there is a type in which a piston rod of the strut assembly rotates and a type in which the piston rod does not rotate when the strut assembly rotates together with the coil spring on steering operation. In either type, there are cases where a synthetic resin-made sliding bearing in place of a rolling ball bearing is used between a mounting member of a vehicle body and an upper spring seat of the coil spring so as to smoothly allow the rotation of the strut assembly.
The synthetic resin-made sliding bearing generally has a synthetic resin-made lower casing and a synthetic resin-made upper casing superposed on the lower casing, and a sliding bearing piece or a sliding bearing projection is disposed in a space between the lower casing and the upper casing. However, if dust, muddy water, or the like enters this space, there is a possibility that a desired bearing function cannot be obtained. Meanwhile, since the strut-type suspension is fitted at a position where dust, rainwater, muddy water, or the like is directly applied during the traveling of the vehicle, the working environment of the sliding bearing fitted between the mounting member of the vehicle body and the upper spring seat of the coil spring becomes extremely severe. Accordingly, if the outer peripheral side and the inner peripheral side of the space where the sliding bearing piece or the sliding bearing projection is disposed is directly open to the outside, the risk of the entry of dust, rainwater, muddy water, or the like from this opening into the space becomes very high, so that the sealing performance at this portion becomes extremely important. In particular, the aforementioned risk becomes increasingly high with the synthetic resin-made sliding bearing in which the lower casing and the upper casing are formed with the inner peripheral side of the space open downward so as to prevent the stagnation of water in the space.
The present invention has been devised in view of the above-described aspects, and its object is to provide a synthetic resin-made sliding bearing which prevents the entry of dust, rainwater, muddy water, and the like onto sliding surfaces from the outer peripheral side and the inner peripheral side of the space where the sliding bearing piece is disposed, so as to eliminate a decline of sliding characteristics attributable to the entry of the dust, rainwater, muddy water, and the like, thereby making it possible to maintain smooth steering force at the time of the steering operation for extended periods of time.